The document EP 0 325 874 discloses a reaction cuvette allowing determining the coagulation time of a blood sample to be analyzed. To this end, the bottom of the reaction cuvette comprises a curvilinear raceway whose concavity is directed upwards, on which a ferromagnetic ball may be placed and driven in movement.
The document EP 0 325 874 further discloses a method for determining the coagulation time, comprising the following steps:                introducing the blood sample to be analyzed into the reaction cuvette,        placing a ferromagnetic ball on the raceway of the reaction cuvette,        subjecting the ferromagnetic ball to a magnetic field so as to displace the ferromagnetic ball along the raceway in an oscillatory movement,        exposing the blood sample to be analyzed to an incident light beam configured to be substantially tangent to the ferromagnetic ball when it is at the lowest point of the raceway,        detecting at least one light beam transmitted through the reaction cuvette and coming from the incident light beam so as to provide a measurement signal representative of the variation of the amplitude and/or the frequency of the movement of the ferromagnetic ball, and        determining the coagulation time of the blood sample to be analyzed from the measurement signal.        
However, when the variation of the amplitude and/or the frequency of the ferromagnetic ball movement is not due to an increase in the viscosity of the blood sample to be analyzed, but on the contrary to the presence of air bubbles and/or impurities in the blood sample, the coagulation time determined by such a determination method is then incorrect, which undermines the reliability of such a determination method.